The present invention relates to a display device, and more particularly, to a liquid crystal display device capable of preventing gap unevenness around the substrate periphery while ensuring the reliability of the seal portion, even with a narrow frame structure.
A liquid crystal display device includes a TFT substrate in which pixels each having a pixel electrode and a thin film transistor (TFT) are formed in a matrix. Further, a counter substrate is disposed opposite the TFT substrate, in which a color filter, and the like, is formed at the position corresponding to the pixel electrode of the TFT substrate. Further, a liquid crystal is interposed between the TFT substrate and the counter substrate. Then, the liquid crystal display device forms an image by controlling the amount of light transmitted through the liquid crystal molecules for each pixel.
Liquid crystal display device are flat and lightweight and have been applied in various fields. Small liquid crystal display devices are widely used in mobile phones, digital still cameras (DSC), or other portable devices. In the present specification, it is referred to as a liquid crystal display panel in which a liquid crystal is interposed between a TFT substrate and a counter substrate, with a lower polarizing plate attached below the TFT substrate and an upper polarizing plate attached above the counter substrate. Further, a liquid crystal display device includes a liquid crystal display panel, a backlight, and the like.
There is a strong demand for the small liquid crystal display panel with a large display area while keeping the profile small. In order to meet such a demand, the width from the end portion of the display area to the end portion of the liquid crystal display panel is reduced. Thus, it is necessary to have a so-called narrow frame.
A sealing material for bonding the TFT substrate and the counter substrate is formed in the frame area. Further, an alignment film is formed in the display area of the liquid crystal display device to provide initial alignment of liquid crystal. The alignment film is required to completely cover the display area, so that the coated area of the alignment film should be larger than the display area by a predetermined width. However, the bonding strength between the alignment film and the sealing material is small. Thus, if the alignment film is formed on the entire surface of the TFT substrate or the counter substrate, the reliability of the sealing material is reduced.
Thus, in the case of the narrow frame, it is necessary to limit the overlapping range so that the alignment film does not overlap the sealing material, or so as to prevent a major problem in the bonding strength even if the alignment film overlaps the sealing material. Japanese Unexamined Patent Application Publication No. 2007-304452 describes a structure in which a material having low compatibility with the alignment film is formed in the portion where the sealing material is formed on the TFT substrate or the counter substrate, in order to prevent contact between the sealing material and the alignment film, even if the alignment film is formed on the entire surface of the TFT substrate or the counter substrate. Japanese Unexamined Patent Application Publication No. 2011-145535 describes a structure in which a second alignment film, which is formed from other fast drying material, is formed in a bar shape prior to the formation of a first alignment film, in order to provide the profile of the first alignment film formed in the display area.
Incidentally, the alignment process of the alignment film includes two kinds of treatment: rubbing and photo alignment. Japanese Unexamined Patent Application Publication No. 2004-206091 describes a method for using photo alignment to (1) reduce alignment disorder caused by the complex step structure, and (2) prevent the influence of foreign matters or other substances caused by static electricity in the rubbing treatment, disorder in the pile of a rubbing cloth, or by the rubbing treatment.